Intermetallic material and use of this material

ABSTRACT

The invention discloses an intermetallic material consisting of the following composition by weight percent: 10% Al, 22% Cr, 36% Co, 0.2% Y, 0.2% Hf, 2% Ta, 3% Fe, remainder Ni and inevitable impurities. The invention also describes its use as a layer protecting against high temperatures and at locations of thermal turbomachines which are subject to friction or vibration.

FIELD OF THE INVENTION

The invention relates to an intermetallic material and to the use ofthis material as felt and/or as a layer protecting against hightemperatures.

DISCUSSION OF BACKGROUND

The guide vanes and rotor blades of gas turbines are exposed to strongloads. To keep the leakage losses from the gas turbine at low levels, byway of example the rotor of the gas turbine is fitted with a very smallamount of play with respect to the stator, so that a stripping actionoccurs. A honeycomb structure is provided at the stator of the gasturbine. The honeycomb structure comprises a metal alloy which is ableto withstand high temperatures. A further design involves the use ofsmooth, coated or uncoated heat shield segments (HSS) which arepositioned radially opposite the rotating blade at the outer radius. Theblade tip then rubs against these heat shield segments. To prevent theblade tip itself from being abraded, the tip may be coated in order thento abrade the heat shield segments to a greater extent. However, onedrawback of this embodiment is that the coating has only a limitedadhesion to the turbine blade. A further drawback is that cooling-airbores, with which either the heat shield segment and/or the blade may beprovided, become blocked during the frictional action.

It is known from documents DE-C2 32 35 230, EP 132 667 or DE-C2 32 03869 to use metal felts at various locations of gas turbine components,for example at the tip of a turbine blade or vane (DE-C2 32 03 869),between a metal core or a ceramic outer skin (DE-C2 32 35 230) or as acladding of the turbine blade or vane (EP-B1 132 667). However, theseembodiments have the drawback that the metal felt which is used isinsufficiently resistant to oxidation. The increases in the hot-gastemperatures, for example in modern gas turbines, lead to the materialsused having to satisfy ever greater demands. However, the metal felts inthe abovementioned documents no longer satisfy the requirement tocurrent levels, in particular with regard to the required resistance tooxidation. U.S. Pat. No. 6,241,469 B1, U.S. Pat. No. 6,312,218 B1, DE-A1199 12 701, EP-A2 0 916 897 and EP-A2 1 076 157 have disclosed metalfelts which are composed of an intermetallic alloy. These felts consistof sintered and pressed intermetallic fibers, and on account of theintermetallic phases have significantly improved materials propertiesthan the abovementioned materials in terms of strength, resistance tooxidation, deformability and abradability. Metallic high-temperaturefibers have also been described in VDI Report 1151, 1995 (MetallischeHochtemperaturfasern durch Schmelzextraktion—Herstellung, Eigenschaften,Anwendungen) [Metallic high-temperature fibers through meltextraction—production, properties, uses].

SUMMARY OF THE INVENTION

The invention as characterized in the independent claims achieves theobject of improving the materials properties of intermetallic alloysstill further, such that they can be used as a felt or as a layerprotecting against high temperatures on gas turbine components which aresubject to high levels of thermal load. By suitable selection of thecomposition of the intermetallic alloy, it is to have a sufficientstrength, resistance to oxidation, deformability, abradability andsufficient vibration-damping properties.

The present invention also relates to an intermetallic material,consisting of the following composition, by weight percent: 8–15% A1,15–25% Cr, 20–40% Co, 0–5% Ta, 0–0.03% La, 0–0.5% Y, 0–1.5% Si, 0–1% Hf,0–0.2% Zr, 0–0.2% B, 0–0.01% C, 0–4% Fe, remainder Ni and inevitableimpurities, and in particular of (by weight percent): 12% Al, 22% Cr,36% Co, 0.2% Y, 0.2% Hf, 3% Fe, remainder Ni and inevitable impurities,or of 10% Al, 22% Cr, 36% Co, 0.2% Y, 0.2% Hf, 2% Ta, 3% Fe, remainderNi and inevitable impurities.

On account of its materials properties, an intermetallic material ofthis type can advantageously be used as a high-temperature coating forthe turbine blades or vanes or other components, for example.

It is also conceivable for the material to be used as an intermetallicfelt on components which are subject to friction in thermalturbomachines. These components may, for example, be the rotor orstator, the tip of a turbine blade or vane, the heat shield segmentsarranged opposite the turbine blade or vane or the platform of theturbine blade or vane. A further advantage accrues if the intermetallicfelt is covered with a ceramic material, since very good bonding of theceramic material is achieved on the rough surface of the intermetallicfelt. As a result, by way of example, the tip of the guide vane or rotorblade is well protected against the actions of heat and againstmechanical effects caused by friction. A further advantage arises fromthe fact that cooling-air bores do not become blocked through abrasionduring operation, since this is a porous material. Moreover, theintermetallic felt also has sufficient vibration-absorbing properties.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained with reference to the appended drawings, inwhich:

FIG. 1 shows an embodiment of a turbine blade or vane according to theinvention with an intermetallic felt at the tip,

FIG. 2 shows an embodiment of a gas turbine with heat shield segmentswhich are arranged opposite the guide vane or rotor blade and consist ofan intermetallic felt,

FIG. 3 shows a second embodiment of a turbine blade or vane according tothe invention, with the intermetallic felt arranged on the platform ofthe turbine blade or vane,

FIG. 4 shows a variant of the second embodiment of detail IV from FIG.3, with the intermetallic felt arranged between the turbine blades orvanes, on the platforms of the turbine blades or vanes on a supportingsubstructure,

FIG. 5 shows a heat shield segment according to the invention with asupporting substructure in accordance with excerpt V from FIG. 2,

FIG. 6 shows a section through the heat shield segment corresponding toline VI—VI in FIG. 5,

FIG. 7 shows an illustration of the oxidation properties of variousmaterials at a temperature of 1050° C., and

FIG. 8 shows an illustration of the oxidation properties of variousmaterials at a temperature of 1200° C.

Only the elements which are pertinent to the invention are illustrated.Identical elements are denoted by the same reference symbols throughoutthe various figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a turbine blade or vane 1 having a tip 11, a mainblade or vane part 14, a platform 12 and a blade or vane root 13. Thismay, for example, be a guide vane or rotor blade of a gas turbine or ofa compressor. An intermetallic felt 2 according to the invention isarranged at the tip 11 of this turbine blade or vane 1. Theintermetallic felt 2 was based on an Ni—Co aluminide. To achieve asufficient strength, resistance to oxidation and deformability, theelements Ta, Cr, Y have been added. A composition according to theinvention of the Ni—Co aluminide is given in Table 1.

Composition of the intermetallic alloy according to the invention(indicating an Ni—Co aluminide)

TABLE 1 Nickel-cobalt aluminides (details in weight percent) Ni Al Cr CoTa Y Si C La Hf Zr B Fe Remainder 8–15% 15–25% 20–40% 0–5% 0–0.5% 0–1.5%0–0.1% 0–0.03% 0–1% 0–0.2% 0–0.2% 0–4%

The advantage of the intermetallic felts 2 is the significantly improvedresistance to oxidation. FIGS. 7 and 8 show the oxidation of variousmaterials compared to the commercially available nickel-based alloysHastelloy X, Haynes 230, Haynes 214 and the alloy SV349. Table 2 showsthe composition of the tested alloys (IM28 and IM29, in particular).

Composition of tested alloys (details in weight percent)

TABLE 2 Name Ni Cr Co Mo W Fe Mn Si C Al Ta Y Zr Hf La HasteloyX bal 221.5 9 0.6 18.5 0.5 0.5 0.1 0.3 — — — — — Haynes230 bal 22 3 2 14 3 0.50.4 — — — — — — 0.02 Haynes214 bal 16 — — — 3 — — — — — 0.01 — — — SV349bal 13 30 — — — — 1.2 — 11.5 0.5 0.3 — — — IM14 bal 22 — — — 3 — — — 10— 0.2 — — — IM15 bal  9 — — — 1.6 — — — 27 2 0.2 0.2 — — IM28 bal 22 36— — 3 — — — 12 — 0.2 — 0.2 — IM29 bal 22 36 — — 3 — — — 10 2 0.2 — 0.2 —

FIG. 8 shows the increase in weight of the alloys indicated in Table 2in [mg/cm²] over a time of 12 hours at a temperature of 1200° C. Theincrease in weight is plotted as a representative measure of theoxidation of the materials. It can be seen from FIG. 8 that thecomparison alloy Hastelloy X has double the increase in weight evenafter a short time of approx. 100 min to approx. 300 min. As timecontinues, the increase in weight of the Hastelloy X continues to risefurther, whereas the intermetallic felts IM14 and IM15 establish aconstant value of between 0.6–0.8 mg/cm², while the two alloys IM28 andIM29 are lower still. It will be clear that the resistance to oxidationof the intermetallic felts is significantly improved, since a constantoxide layer has formed. The resistance to oxidation is one of the mostimportant factors for the service life of the component as a whole forthe use according to the invention of the intermetallic felt atlocations of a thermal turbomachine which are subject to friction. Thetwo alloys IM 28 and 29 differ from the other alloys by, for example,their Co content. This increases the resistance to oxidation of theintermetallic material still further.

FIG. 7 shows an illustration that is comparable to FIG. 8, but with thetests carried out at a temperature of 1050° C.

To increase the strength of this turbine blade or vane 1 as shown inFIG. 1 still further at the tip 11, the intermetallic felt 2 may becovered with a ceramic material 3, for example with a TBC (thermalbarrier coating). TBC is a Y-stabilized Zr oxide. However, equivalentmaterials are also conceivable. The ceramic material 3 may be sprayedonto the intermetallic felt 2, and the uneven surface of theintermetallic felt 2 means that the ceramic material is very securelyheld thereon and provides a good resistance to oxidation. The ceramicmaterial 3 offers good protection against thermal and mechanical, forexample friction-induced, effects. Cooling-air bores which may bepresent in the turbine blade or vane 1 or at the rotor/stator 4advantageously cannot become blocked, since the intermetallic felt 2 isa porous material.

FIG. 2 illustrates a further embodiment. FIG. 2 diagrammatically depictsan illustration of a gas turbine having a rotor 4 a, and a stator 4 b.Rotor blades 6 are secured to the rotor 4 a, and guide vanes 7 aresecured to the stator 4 b. Heat shield segments 8 are usually arrangedopposite the guide vanes/rotor blades 6, 7 on the rotor 4 a or stator 4b, respectively. According to the invention, these heat shield segments8 may likewise partially or completely comprise an intermetallic felt.The porous properties allow improved cooling at this location even ifabrasion has occurred, since the porous structure of the intermetallicfelt prevents blockages. As has already been described, the abrasion maybe reduced by a layer of TBC. The component may also be cooled beneaththe TBC layer, since the cooling medium can escape laterally through theporous felt.

FIG. 5 shows a heat shield segment 8 according to the inventioncorresponding to excerpt V from FIG. 2. The intermetallic felt 2 hasbeen placed on a supporting substructure 5. The supporting substructure5 has securing means 9 which are used to secure it to the rotor 4 a orstator 4 b (not shown in FIG. 5). The lateral securing means 9 areconnected to one another by struts 10. On the side which faces theturbine blades or vanes, the intermetallic felt 2 is inserted betweenthe struts 10 and mechanically connected to it. This connection can beeffected, for example, by soldering, welding or casting. For durabilityreasons, the felt should be cohesively secured to the supportingsubstructure 5.

FIG. 6 shows section VI—VI from FIG. 5. It can be seen from thesectional illustration that the struts 10 which connect the two securingmeans 9 do not penetrate through the intermetallic felt 2, but ratherthe intermetallic felt 2 is merely secured to them. As can be seen fromFIG. 6, to further increase the thermal stability of the heat shieldsegment 8, the intermetallic felt 2 may in turn be covered with aceramic material 3, for example with a TBC (thermal barrier coating).However, equivalent materials are also conceivable. As in the case ofthe turbine blade or vane 1 shown in FIG. 1, a cooling action isretained even in the event of abrasion, since the intermetallic felt 2does not become blocked.

For improved cooling, in the exemplary embodiment shown in FIG. 3, theintermetallic felt has been placed on the platform 12 of the turbineblade or vane 1 of the thermal turbomachine. In this case too, it isappropriate, as has already been described in connection with FIGS. 1,2, 5 and 6, for the felt 2 to be covered with a ceramic material 3. Thishas the advantage that the TBC bonds particularly well to theintermetallic felt and the felt is resistant to oxidation. There is noneed for an additional bonding layer (e.g. MCrAIY). This is illustratedin FIG. 3 in addition to the straight turbine blade or vane 1. The TBCalso serves as a protection against wear.

FIG. 4 shows a second variant of the exemplary embodiment of detail IVfrom FIG. 3. The intermetallic felt 2 is secured, between two turbineblades or vanes 1—on the platform 12 of the turbine blade or vane 1—to asupporting substructure 5, comprising a cast metal part or some othermetal. The supporting substructure 5 may also comprise various chambersin order to ensure an optimum supply of air to the intermetallic felt 2.

The intermetallic felt can also be used at locations within the gasturbine which are subject to vibrations, since in addition to beingresistant to oxidation as described above, the felt also has very goodvibration-damping properties.

On account of its materials properties, an intermetallic materialaccording to the invention may advantageously also be used as ahigh-temperature coating 15 on the turbine blades or vanes or othercomponents. As can be seen from FIGS. 8 and 7, the two alloys likewisehave improved properties with regard to oxidation when compared to thealloy SV 349. The prior art has disclosed various coating processesallowing the protective layer to be applied to a turbine blade or vaneof this type, for example a plasma spraying process. In this case, ametallic powder consisting of the material that is to be applied isintroduced into a flame or a plasma jet. This powder melts at thatlocation and is sprayed onto the surface that is to be coated, where thematerial solidifies and forms a continuous layer.

A physical (or chemical) vapor deposition process is also possible. Inthis process, solid coating material in block form is heated andevaporated (e.g., using a laser or an electron beam). The vaporprecipitates on the base material, where after a suitable time it formsa coating. Other equivalent coating processes are also conceivable.

1. An intermetallic material, consisting of the following composition,by weight percent: 12% Al, 22% Cr, 36% Co, 0.2% Y, 0.2% Hf, 3% Fe,remainder Ni and inevitable impurities.
 2. An intermetallic material,consisting of the following composition, by weight percent: 10% Al, 22%Cr, 36% Co, 0.2% Y, 0.2% Hf, 2% Ta, 3% Fe, remainder Ni and inevitableimpurities.
 3. A method of using the intermetallic material as claimedin claim 1, comprising steps of coating at least a portion of a thermalturomachine with the intermetallic material.
 4. The method of using theintermetallic material as claimed in claim 1, comprising steps offorming a felt comprising the intermetallic material on components whichare subject to friction in thermal turbomachines.
 5. The use method ofusing intermetallic felt as claimed in claim 4, wherein theintermetallic felt is disposed on a rotor or stator.
 6. The method ofusing the intermetallic felt as claimed in claim 4, wherein thecomponent is a turbine blade or vane, and the tip of the turbine bladeor vane is provided with intermetallic felt.
 7. The method of using theintermetallic felt as claimed in claim 4, wherein the component is aturbine blade or vane and the platform of the turbine blade or vane isprovided with the intermetallic felt.
 8. The method of using theintermetallic felt as claimed in claim 4, wherein the component is aheat shield segment made partially or completely from the intermetallicfelt.
 9. The method of using the intermetallic felt as claimed in claim4, wherein the intermetallic felt is covered with a ceramic material.10. The method of using the intermetallic felt as claimed in claim 4,wherein the felt is used on components which are subject to vibration inthermal turbomachines.